Being aged, and rotund (before I started LCHF), I was idly computing my friends' BMI. I started calculating what my BMI would be if I remained my current 6ft 1" height, but reduced to their current weight (It will happen eventually, given my current success). What we learned was that if I reach their current weight, my BMI would be as much as 3.5 BMI less than they CURRENTLY are. This has caused more than one to review their current diet for improvement